1. Field of the Invention
The invention relates to a method and apparatus for the fusion jointing or joining of pipe parts having a small diameter, and being made of a material such as polyvinylidene difluoride (PVDF). Pipes made of other plastics, such as polyvinylchloride (PVC), clean polyvinylchloride (CPVC), polyethylene (PE), polypropylene (PP), ethylene chlorotrifluoroethylene (ECTFE), perfluoroalkoxyalkane (PFA), polyether ester ketone (PEEK), polyphenylene sulphide (PPS) or the like can also be jointed to one another according to the invention.
2. Description of the Related Art
The use of so-called electric sockets in the fusion jointing of pipes made of high-density polyethylene (HDPE) is known in the art. In this operation, the axially aligned pipe parts to be fusion-jointed are linearly aligned, maintaining a certain gap at a butt joint into which a ring made of the same material as the pipe parts to be fusion jointed can also be inserted. The electric socket is arranged around the butt joint, and heated by means of the electric heating element held therein. This causes a softening of the plastic at the socket/pipe parts interface, and consequently a fusion jointing of socket and pipe parts. However, a smooth fusion jointing does not take place between the pipe parts along the pipe gap on the inner diameter of the pipe. The gap remains in practice and consequently contributes to a relatively pronounced disturbance of the flow which will occur in the jointed pipe parts during use. In addition, in many cases the electric heating element is exposed in the region of the pipe gap and is therefore subject to corrosion.
Until now, the technique described of fusion jointing in HPDE pipeline construction with comparatively large pipe diameters could not be used in the fusion jointing of PVDF pipeline systems with their relatively small diameters. In the case of PVDF pipes, owing to the small diameters mentioned and the associated small wall thicknesses, when the known electric-socket fusion jointing is used, the pipe parts tend to collapse when heated, which has the effect that a reliable, durable, reproducible fusion joint quality cannot be obtained.